Does wood change its colour?
Natural oxidation.

Changes in colour over time are the effects of oxidation typical of live organic matter like wood and caused by the natural interaction between its component elements with air and light. The dynamics of colour change differ from wood to wood. Light European species, (such as oak, cherry, maple, ash, etc...) tend to have a rather slow alteration rate that enhances the warmer, amber shades. Most exotic woods are usually associated with darkening, sometimes quite quickly and drastically (for example, doussie and iroko).

Other species have specific and unusual reactions, like teak, where the darker parts tend to lighten and even out over time. As a result of oxidation, wood subjected to heat treatments tends to lighten with time. Changes in colour also depend on the finish any particular wood was treated with. These phenomena are associated with the very nature of wood and have always been part of its beauty. Small gestures can be of great help. The periodic moving of rugs will, for example, even out covered areas that usually don’t get sunlight. Hanging or closing curtains, putting up UV screens in front of the windows that get the most sun will prevent any real, long term damage to the wood.